1. Field of the Invention
The present invention relates in general to Pseudomonas sp. YS-180 having a capability of producing docosahexaenoic acid (hereinafter called "DHA") and a method for the production of DHA using such a microorganism. More particularly, the present invention relates to a method comprising screening, from intestines of fish, a microbial strain, Pseudomonas sp. YS-180, that effectively produces DHA, as one of its unsaturated fatty acids, investigating the morphological, culturing and physiological characteristics of the screened strain to isolate and identify, and establish optimal conditions for the production of DHA.
2. Description of the Prior Art
DHA is an unsaturated fatty acid that has been of keen interest since an epidemiologic survey employing Eskimos as subjects of the survey at the 1970's. This is associated with phospholipids, such as phosphatidyl ethanolanine (PE) and phosphatidyl serin (PS), present in the grey matter of the human frontal lobe, while having inherent physiological functions connected with the brain and retina. In addition, DHA is highlighted as a health food due to various efficacies, such as anti-trombus, antihypersensitive, anti-arrhythmic, and anti-camcer properties. However, DHA is not easy to synthesize chemically, and thus, it is currently obtained from natural material. Till now, such a highly unsaturated fatty acid has been industrially extracted from oils of fishes having a blue back, such as mackerel, saury, bluefin tuna, horse mackerel, and herring.
Fish oil fatty acids often originate from marine microorganisms, such as algae and vegetable plankton, which are ingested by such fish. However, it is problematic in that DHA extracted from the fish oil is unsuitable for the use as foods and medical supplies when the fish is contaminated with an environmental pollution material. Another problem is that it is difficult for DHA to be produced in a stable way. Additionally, another problem is that DHA has an offensive fish odor. Consequently some researchers have predicted that, in addition to being present in fish oil, DHA-producing strains could be also present in the intestine of the fishes having the blue back. Therefore, bacteria isolated from an intestine of a variety of fishes and marine animals were cultured and examined for a DHA-producing capability. As a result, many kinds of DHA-producing strains wvere isolated. Marine microorganisms reported producing EPA and DHA, simultaneously include Isochrysis galbana, Dinoflagellate sp. and Crypthecodinium cohnii of Chrysophyceas genus.
There are current investigations to produce EPA and DHA from bacteria or algae in large quantities using biotechnology. Examples ofthese studies include Watanabe et al., "a fatty acid composition of an EPA product from marine bacteria", J. Mar. Biotechnol., 4, 104-112, 1996; Baumann et al., "a possibility to produce EPA from novel microorganisms of the South Pole", Int. J. System, Bacteriol., 47, 1040-1047, 1997 Bico et al., "fatty acids from marine plants", Phytochemistry, 34, 1521-1533, 1993; PCT publication WO 91/11918 (1991) concerning a DHA production; Yamajaki, "a production and use of EPA by marine bacteria", Bio Industry., 6, 491-501, 1989; and Kazo et al. "Composition of fatty acids and lipids of a novel DHA product" Lipids. 32, 9 p. 975-978, 1997. However, these studies are only basic investigations concerning the production of DHA and EPA from microorganisms.